Hardening process



20 from 24 hours to 90 hours.

Patented Feb. 18, 1930 UNITED STATES PATENT OFFICE AUGUSTUS B. KINZEL, F BAYSIDE, YORK, ASSIGNOItTO ELECTED METALLURGI- CAL ., A CORPORATION or wns'r vmeinm nannnmne rnocnss a hard nitrification case in a minimum length of time, and for another, the provision of a new nitrification case hardening process, and a new material for the operation thereof.

It has been found that by the diffusion I of active nitrogen at relatively low temperatures into and through a surface layer of a ferrous material object having certain alloy constituents, a hard and durable case or surface layer is obtained. This processis desirably carried out at temperatures below.

about 600 C., and is customarily done by heatingthe metal part'to theappropriate temperature in an atmosphere of gaseous ammonia, over a period of time, ranging My invention provides a new means and process for producing a harder, tougher and more ductile nitrification case upon a ferrous object in a much shorter period of time.

In practicing my .invention I provide a molten nitrification bath as distinguished from the prior art which provided the nitrogen from a gaseous atmosphere. I provide preferably a molten bath of the mixed cyanides of sodium and potassium, having such a composition that a low melting point is obtained. I then immerse the object to be case hardened within the molten mixed cyanides, being careful to keep the temperature (below 580 C. The case hardening proceeds rapidly and in about 2 hours may produce a hardened nitride case having a thickness of about 0.001 inches. 7

It may be noted that this is a broadly dif- 40 ferent process'from prior methods of case hardening with cyanide baths in which a temperature well above 700 (1., is always reached, and a carburization case only is produced. In the process of my invention no carburization occurs at the low'tem'peraturebut only a nitrification. f

The resulting case obtained by the process of my invention is substantially harder than thecase obtained by the prior nitrification process, and is also more ductile. When pro- 1928. Serial No. 288,816.

duced upon a given suitable alloy, it has a hardness about four times as great as that produced by the previous nitrification process upon the same alloy, and it is also sufficiently ductile to permit'of considerable distortion, since pressure by a point or small ball upon the treated object does not crack or shatter the case hardened coating as occurs with. nitrification cases produced by the methods of the prior art, which are'much less resistant to deformation and pressure.

In the preparation of thecase hardening bath of my invention, I find it convenient to provide a mixture of about 58% of sodium 7 cyanide and about 47% of potassium cyanide, this mixture producing the eutectic, or lowestmelting composition and fusing at about 445 C. This bath is thus fluid over a convenient temperature range below the criticalpoint at 580 C.,"at which transformation of the nitrification product begins to occur. By the process as above described I am thus enabled to treat a ferrous object for case hardening to obtain a newand useful product with a saving of time, and cost. The process is particularly advantageous because of the low temperature at which it operates whereby the object may be given suitable heat treatments for the production of desired physical characteristics and may thereafter be case hardened without change in the characteristics of the body or danger of deformation or internal strains.

ing of maximum hardness is obtained without the necessity for any subsequent heat treating steps to temper the case.

As abath for the operation of the process Likewise a casof my invention I have, above, disclosed a mixture of sodium and potassium cyanide. It is not however, necessary that such a mixture be used since-there are various other mixtures which obtain a similar result. For instance, mixtures of other cyanides such as sodium cyanide and zinc cyanide, or potassium cypoints sufliciently low to bev useable for the amide. and magnesium cyanidewr vice versa,, produce eutect c mlxtures havmg meltlng' process of my invention. Alternatively,"

other substances than cyanide may be used, such for lnstance, as a nnxture of aconvement cyanide and a' cyanamide. Likewise other salts which produce the "desired reduction in melting point may be used althoughit is preferable'that substances which evolve-oxygen be excluded. I

The process of my invention is particularly applicable'to alloy steels,- such'as those -con-' 'taining vanadium or aluminum, as well as such elements as manganese, silicon and chromium, and such alloy steels are the preferred materials for treatmentby my process. The

alloys containing the vanadium and aluminum produce cases having a maximum hardness and may be made sufiiciently hard to scratch glass readily. The alloys containing ,manganese; silicon and chromium, also produce a substantial degree of hardness al-v though less than the first two mentioned a1- loying elements when treated by the process of my invention. In each case however, a

v substantial gain in hardness and ductility appears over 'a nitrified case made according to p the prior art.

The hardness obtained by the process of my invention is conveniently indicated by measurements, in terms of microcharacter units, as made upon a suitable steel. Comparison was madebetween the hardness obtained by the previously used gaseous ammonia nitrification process, and by the process of my invention, upon four typical steelshaving the Samples of .the same alumimicrocharacte'r units.

steels-treated in the bath of my invention gave surface hardness values varying from 600,000 to 800,000 microcharacter units.

' By the process of my invention I have thus produced a new and simple means of obtaining a case hardenedsurface upon ferrous objects, which is much sim ler to operate, and

much more rapid and e ective than the previous methods.'

While I have described several embodiments of the process of my invention it is capable of still other embodiments, adaptations and modifications without departure from the spirit thereof and I desire therefore that only f1,747,54'e I nitride casing, with a liquid non-oxidizing nitrogen-containing salt at a temperature below 600 C.

2. The process of case-hardening ferrous articles which comprises treating an article having a surface composition adapting it for nitride casing with a liquid cyanide at a temperature below 600 C.

3. The process of case-hardeningferrous I articles 7 which comprises treating an article having a surface contalnmg vanadium and of a composition adapting it for nitride casing with a liquid cyanide at a temperature between 445" (land 600 C.

In testimony whereof, I aflix my signature.

AUGUSTUS B. KINZEL.

- such limitations shall be imposed upon the 1 appended claims as are indicated therein, or required by the prior art.

I claim as my invention:

.1 The process of case-hardening ferrous articles which comprises treating an article having a surface composition adapting it for 

